Automatic circuit breaker



Feb. 27, 1940. w. JENKINS 2,191,665

AUTOMATIC CIRCUIT BREAKER Filed Jan. 13, 1939 ATTORNEY.

APlanted Feb. 21, i940- t 2,191,665 AUTOMATIC CIRCUIT BREAKER Wayne E. Jenkins, Los Angeles, Calif., assignor to Domestic Manufacturing Company, Inc., Los Angeles, Calif., a corporation of California i Application January 13, 1939 Serial No. 250,785 5 Claims. (Cl. 20o-138) oli/FICE 'I'his invention relates broadly to automatic temperature-responsive devices and has to do more especially with contact makers and breakers which operate automatically in conformit 5 with predetermined temperature changes.

'Ihe object of this invention is to provide a durable and reliable, but inexpensive safety accessory for use in conjunction with gas and oilfired furnaces and the like, havingvpilot burners the main burner automatic fuel-control valves are electrically actuated-the function of the,

, safety accessory being to open the main burner fuel-control circuit in event of a` failure of the il pilot llame and tc keep said circuit open until the pilot llame is re-established--thuspreventf ing the gaa or other fuel being turned on when there is no pilot flame to ignite it. Probably the simplest, cheapest and most com- 20 pact type of thermostatic element ever devised is the lfamiliar bi-metallic plate, consisting of two different metals, superimposed and having different expansion coeiilcients. But velements l of that kind have not heretofore been considered practicable for subjection to considerable temperatures (such as the temperature prevailing in or immediately adJacent a pilot flame) because at such temperatures .they lose, in' whole or in part, their elasticity and cannot then be suby N jected to ilexurewithout being permanently deformed. And since the usefulness of a thermostatic element is generally dependent upon its ability fully to restore itself to its initial form or distorting force applied to the thermostatic element when its temperature is such as to cause its elasticity to be materially impaired or destroyed-the force tending to distort being applied to the Velement only when its temperature is low enough to ensure against permanent distortion. How this-is accomplished can best be explained by reference to the drawing and conso temporaneously with the detailed description of the device illustrated.

Another feature of my present invention'is the outgrowth of great diillculty which I experienced in developing a spring-actuated device which is 58 veryA compact and and at the same timel capable of withstanding the high temperature to whichv it normally is subjected in operation-due to its y tried and which could conveniently have been utilized in thespace available were found to be unworkable because they lost their temper and ceased to be springs. But after protracted trials l .discovered a solution to this difficulty in the provision of a leaf spring so situated as to be 10.

partly protected from the heat pf the pilot flame and so supported that the heat. which it receives is rapidly conducted away-thus keeping the 1 invention;

Fig. 2 is a sectional view taken along' the line 2-2 of Fig. l and showing the contacts open;

Fig. 3 is the same as Fig. 2 except that the' pilot is lighted and the contacts closed;

Fig. 4 is an enlarged section taken along the 30 line 4-4 of Fig. 1; an'd Fig. 5 is a detail view taken along the line 5-5 of Fig. 2.

I and 2, respectively, are contact points which are included in lthe'control circuit of an elec- 8 5 trically operated valve (not shown) which con- Atrols'the flow of gas or other fuel to the main burner (alsov not shown) of a furnace or other heating device. Said contacts are continuously closed so long as the pilot remains lightedand 40 -are intended to open automatically'if and when the pilot flame is extinguished. And, when open, they serve toprevent opening of theN main fuel valve by interrupting its vactuating circuit. Con tact point 2 is fixed, being welded to the end of 45 a screw 3, which is a component part of a binding post 4, to which a conductor 5 is 'shown connected. Binding post l and screw I are insulated from the frame casting -which latter is provided with two holes 1 and 8 by means of 50 which vit may be mounted on amain burner or other convenient support.

Frame casting B is provided with an opening at l for the reception of a pilot tube l0, which is held in place by means of a setscrew Il,` l(ias is supplied through a conduit I2 to the pilot tube, and the latter is orificed at its upper end. to form a burner tip. In Fig. 3 the pilot name is depicted at I3.

Frame casting 6 includes two parallel, vertical members 6a and 0b which are connected by cross-pieces 8c and 6d.

Bridged between cross-pieces Bc and 6d and secured thereto by screws I4 is a plate Il which I shall refer to as an abutment plate because it serves as an abutment for a thermostatic element IB-which is a bi-'metallic strip, normally bowed, as per Fig. 2, and curved at its two extremities where it abuts plate I5.

Thermostatic element I6 is not attached to abutment plate I 5, but it is bifurcated at its upper end, that is at Isa, so as to straddle a pin I1 which .is pressed into abutment plate I5 and serves `to secure element I6 against rotation about its shaft I8.

Element I8 is rivetally secured to one end of shaft I8, together with a strip of stainless steel I9 which serves as a shield between the pilot llame and the thermostatic element, so as to prevent the name impinging directly upon the latter.-

Shaft I8 is a loose t in a bushing 20 which is rivetally secured to plate J5 and said shaft is slidable axially in said bushing, as well as being rotatable therein.

Anchored to the upper cross-piece 8c by means of screws Il and nuts 2I is a contact arm 22, consisting of a strip of stainless steel, to which contact arm is secured the contact point I.

I A stainless steel leaf, spring 23 is secured at its 1 lower end between cross-piece 6d and abutmentv and in order that it may plate I5, and itsfree upperl end bears [against contact arm 22, tending continuously to moveV the latter toward the fixed contact 2 so as to bring the two contact points into` engagementas shown in Fig. 3.

, A small pin 2l extending transversely of and carried by shaft vI8 engages the back surface of is then able to flex contact arm 22 to the closedcontact position, per 3. Ii' heated still further, element I6 will assume a curvature op- 4 posed to the normal curvature shown in Fig. 2;

d do so without interference, shield I9 isjhcurved as shown.

'I'he thermostaticelement is so proportioned I that it will completely straighten out before it gets hot enough for its elasticity to become impaired; and when thus straightenedout, it no i longer bears against the abutment plate I5 at its y extremities and the only force then acting uponv device inoperative-as will be self-evident.

In the development of the present device, one of the major problems encountered was the provision of a spring for actuating the contact arm. which would not be impaired bythe prevalent high temperature. and with which simplicity of design and compactness could'be achieved. A

-coil spring surrounding shaft I! would get too hot and therefore lose its temper. And the same thing would happen to the contact arm if that were to be employed as a spring. But, after much discouraging experimentation, I ultimately discovered that by securing the leaf spring 2l to` the frame casting at a point well below the pilot flame and'situating it behind the abutmentplate II--where it is partially shielded from the pilotthe heat which it receives is conducted away rapidly enough to ensure that the spring will not lose its temper.

The device of the present invention has to be sold, if at all, in a highly competitive market where price is a controlling factor; and at the same time it must be completely dependable in operation for a long period of time. Otherwise expressed, the device must be as dependable as it is possible to make it, regardless of price and substantially as cheap to manufacture as the lowest pricedrcompetitive device. For that reason, costly parts and machining. operations must be avoided as far as possible, and the design must be such as to reduce the assembling, testing and adjusting operations to a minimum for these all enter into the cost of production.

'It will be observed that, Save for one light casting, involving the simplest of machining operations, all the components of my device are simple punchings and screw machine parts; and it will be apparent that the assembling operations entail very little labor. And, in this connection, one outstanding feature which I wish to point out is that the elements I5, I6, I8, I0, k20 and 2| constitute a Self-contained unit which is separately assembled before mounting on the framecasting, and that the contact arm 22 is provided with an oblong opening 25 (see Fig. 5) which permits insertion therethrough of the end of shaft I8 and pin 24, when turned at an angle of ninety degrees fromV the normal position shownin Fig.' 5. The nal assembly is thus greatly simplified because it is much easier to insert the pin A24 in shaft I8 before mounting plate I5 on the frame casting than to do so afterward. Y l

What is claimed is:

l. A temperature-responsive device compris-- toward said abutment, said strip being free to L uassume a curvature opposite to its normal curvature and having a tendency so to do in response to rising temperature.

2.' A device in accordance with claim l wherein the said supporting member constitutes the sole supporting means for said strip.

3. A device in accordance with claim 1 wherein the said supporting member is a shaft .iournaled lto slide axially and having one end secured to said strip approximately midway between the' two extremities thereof and wherein said spring is a leaf spring, said spring'being situated-be- 15 hind said abutment and anchored at a point somewhat remote from said strip, the i'ree end of said leaf spring being operative upon said shaft.

4. A temperature-responsive device comprising: an abutment plate. a bowed bi-metallic strip the twov extremities of which normally bear against one side of said plate, a shaft journaled in and extending transversely through said plate,

said shaft being movable axially relatively to said plate and having one end secured to said stop midway between the extremities thereof, a leaf spring situated behind said abutment plate and operatively acting upon said shaft so as to continuously urge said strip toward said abutment plate, and mechanism to be actuated in 'conformity with temperature changes affect# 5. A temperature-controlled automatic circuit-breaker including a pair of contacts at least one of which is movable to make and break contact with the other, said .circuit-breaker comprising a frame, a movable contact arm supported by said frame and carrying one of said contacts, the movements of said contact arm serving to make and .break contact, a bowed bi-metallic strip, an abutment plate attached to-said frame and-interposed between said strip and said contact arm, the two lextremities of said strip normally bearing against said abutment plate, a shaft journaled in said abutment plate and extending laterally therethrough, said shaft being slidable axially, said shaft being secured to said strip intermediate its extremities and constituting the sole support for said strip, said shaft being connected with said contact arm, a leaf spring continuously urging said contact arm, together with said shaft and said strip, in a direction such as to bring about interengagement of said contacts and also to press the extremities of said strip against said abutmentthus permit said .leaf spring to movesaid cong5 tact arm toward its closed-contact position.

WAYNE E; JENmNs. 

